System for controlling electromotors.



G. KRAMER.

SYSTEM FOR CONTROLLING ELEGTROMOTORS.

APPLICATION FILED 11.12.11, 1910.

1,048,548; Pate nted Dec.31, 1912.

-, UNITED STATES PATENT o IoE.

CHRISTIAN KRAMER, E FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR To THE Exam 0F FELTEN a GUILLEAUME-LAHMEYEBWERKE AKTIEN-GES'ELLSCHAFT, 0F EnANKroR'r-oN-rHE-MAIN, GERMANY. v

sYs'rEEr on CONTROLLING ELECTROMOTORS.

Specification of Letters Patent.

Patented Dec. 31, 1912.

Application filed March 11, 1910. Serial No. 548,738.

To all whom it may concern:

Be it known that I, CHRISTIAN KRAMER, a

subject of the German Emperor, and a resi ed claims.

For thepurpose, of explaining the inven* tion several examples embodying the same have been shown in the accompanying drawings, in which the same letters of reference have been used in all the views to indicate In said drawin s Figure 1, is a diagram illustrating the e ectof a compound wlnding in a Leonard connection, whereby an electromotive force is produced which balcircuiting the field winding of the controlances the electromotive force consumed in.

the resistances of the system, Fig. 2, is a diagrammatical view of the improved system in which controlling means for the exclta- 'tion of the shunt fieldare provided. Fig. 3,

is a diagrammatical view ofa modification of the system shown in Fig. 2, in which the field' excitation is changed, Fig. 4, is a diagrammatical view ofa modification of the systems shown-1n Figs. 2 and 3,'in Wl'llCh means arelprovided for weakening or shortling dynamo, and Fig. 5, shows a further modification of the systems illustrated in Figs. 2 to 4, in which the controlling generator is dispensed with, and in lieu thereof the electromotive force of the driving motor 'is used as a controlling electromotive force.

As is. well known in the art, by means of the Leonard connection the speed of electromotors can be regulated within large limits, and the saidregulation is almost independent of the-load 'of the motor, because the electromotive force of the starting'dynamo 1s increased at a rate which is proportional to residual magnetism of the starting machine its excitation. This regulation which is suf ficient in most cases is aflfected merely by the and by the loss in the voltage which takes place in the starting machine, in the circuit, and in the armature of the driving motor. In most cases the efiect of these influences is very small. But in some cases in which the regulation must be very accurate, for examole in 'motors for driving paper making machines, motors for driving armored turrets,

and the like, the said influences are objectionable. The reason for this will be readily understood from the following consideration: If the loss in voltage be assumed to be, 5%, with a field excitation of 5% the unloaded motor will have a speed which is equal to'5% of the maximiun speed, while 4 ordinate indicates the electromotive force of the starting machine as a function of the strength of the current. The heavy line in- I 'dicates the electromotive force which is produced by the series field, and which therefore rises at'a rate proportional to the current. If the value of the said electromotive force were increased exactly atthe' same rate as the loss in voltage is increased upon an increase of the current, a state of equilibrium would be produced for each value of the current. If to the electromotive force of the shunt or main field the said electromotive force of the series field is added which in the diagram has been indicated by the letters 6 f, the driving motor must have thesame speed for each strength of the current and therefore under any load, because then its speed depends exclusively on the-electromotive force of the shunt excitation. i

If it were possible to construct. a machine in which there is no remanence whatever, such a machine would work satisfactorily.

However, as there is nosuch machine, a melimits, and particularly can not be stopped,

even if the value of the shunt excitation be zero. In order to assure a satisfactory operation, in such apparatus thevalue of compounding was heldconsiderably below the value which would have been necessary in order to compensate the ohmic loss in voltage, and in order to completely stop the entire apparatus it was necessary to breakthe main circuit. J

The object of the present improvements is to provide a system in which the afore said injurious influences are avoided. For this purpose a. controlling device is provided which independently of the main current tends to hold the speed of the driving motor exactly equal to the value which it must have by reason of the excitation of the shunt field, and which in case of a divergence automatically regulates the shunt field. Fig. 2 shows a diagrammatical view of a system embodying the invention. The starting machine has been indicated by the letter a, its compound winding by the letter 0, its shunt or main field windingby the letter f, the regulating device for the latter by the letter 1', and the driving motor by the letter on. The field winding 9- of the latter is separately excited. V

To thedriv'ing motor m a generator at is coupled the field h of'which is also separately excited and which is always under its full excitation. rent consumed by the motor m the generator 03 produces an electromotive force which is exactly proportional to its speed.- Thereby a means is provided by which to examine whether or not the electromotive force of the generator has a value which is exactly proportional to the field exciting currentof the starting machine a. If this is not the case,.the difference between the actual value of the electromotive force and that which it should have is made use of to influence the said current of the field wind- A further method consist V providing "*ifield windin rheostat in the circuit of t and regulating the loss of voltage in the said rheostat by means of the controlling generator in such a" way that a balancing cur rent is set up whenever the aforesaid values fiare not the same.

This balancing current can be used for changing the field for example by causing the same to flow through the shunt field winding f of through a sedond Independently of the cur-- subsidiary field winding of the starting generator. Fig. 2 shows an examplein which the balancing current is caused to flow through the shunt field winding f, and this example will now be described.' v

The resistance r is connected to a source of electric energy. To the positive pole of the said source there are connected the field winding f and in series therewith a rheostat swhich is adapted to be connected to the rheostat r by means of the regulating device. In" the example shown the source of electricity consists of a battery which may have a strength of 100 volts. If the rheostat r has a resistance of 100 ohms, the field winding a resistance of 50 ohms, the rheostat s alsoa resistance of 50 ohms, and if the regulating lever is so set as to divide the resistance of the rheostat r in the proportion of 99 to '1, the current passing through the field winding f and the rheostat. s is about one hundredth of that which passes through the rheostat' 1', that is about 0.01 ampere.

' This current causes a loss in voltage within the rheostat's which amounts to 0.5 volt. If the motor m and therefore also the generator d revolve exactly at such a speed, as toproduce an electromotive force of 0.5 volt, there will be no balancing current. If however the remanence of the starting machine-acts for example in a negative sense. and the motor is at rest, the generator (I does not produce any electromotive force at all and it acts as if the rheostat s were sho'rt-circuited. Therefore the current of the field winding is increased to about its double value. and the electromotive force will be afif'ected in such a way,-as to cause the motor to start. If however the remanence acts in a positive sense, and the speed of the motoris above the normal, the electromotive force produced by the generator will .be more than 0.5 volt, so that thecurrent of the field winding f is reduced and the speed of the motor is likewise reduced by the "decrease of theexcitation :of the starting machine a. p It appears therefore, that the eflectof the arrangement is to bring the speed of the moi" tor m in harmony with the exciting current of the shunt field winding f of the starting machine a, and that the said eflect is so much the greatervthe greater the ratio of the resistance of the rheostat s to the ohmic value of the field winding f is. This'conisideration is the reason for thearrangement I shown in'Fig. 2; but it fshould be understood, that the example shown is not a prerequisite for the desired effect. When'the starting machine a is excited to its full ca-. pacity, the correcting means is not required,

because then the percentage differences are naturally small. It can therefore gradually be thrown out of, operation the more the excitation approaches this maximum 35 a rately excited. The field f of the starting figure is tions the resistance of the rheostat s is.

Therefore the arrangement shown in the preferably used, in which upon an increase of the excitation of the field windduced, while u on a decrease of the excitation of the fie d winding 1 the said resistance is increased. This arrangement is also advantageous since in case of full speed the controlling generator 0! has to supply a comparatively small amount of energy, and on the other hand in case of full excitationthe exciting energy of the field can also be kept small, because in this case no energy is wasted in rheostats. It is of minor importance from whence the controlling electromotive force is supplied, and instead of being taken from a special generator which is driven by the motor m, it might just as well be produced by means of a special Winding provided on the motor.

f the resistance of the rheost'at 8 is re- The arrangement so far described can be modified by controlling the field of the starting machine in such a way, that upon an increase of the load the field of the starting machine is weakened, so that the strength of the current can not be increased beyond a certain maximum value. An example of such a system is shown in Fig. 3 of the drawings, As shown the-starting machine a is directly connected with the working motor m. To the latter the controlling generator d is coupled which may also be sepagenerator (1 can be, excited to any intensity by means of a rheostat r. Through the intermediary of an adjustable rheostat s the controlling generator (I is so connected to the field j, that at a certain number of revolutions its voltage corresporids to the voltage at the terminals ofthe field winding f.

The operation of the system i-s'as follows: While the motor m is under its normal load, it will assume such a speed under the influence of the starting generator 'a or the excitation of the same that the voltage of the controlling generator d substantially bal:

- field winding ,1 traverses the controlling;

ances the voltage of the field. .If the motor has its maximum speed, and only its load is abnormal, its speed is decreased. By this decrease in the numbenof revolutions the voltage of the controlling generator (1 is decreased, and a branch current which' under normal conditions passes through the generator d. Thereby the intensity of the field f is decreased. The speed of the working motor is further reduced, and the parts can be so arranged, that for a certain maximum current the motor is stopped.v This is the case if the resistance of the circuit of the controllinggenerator is such that when the controlling generator is at rest only so much current traverses the field winding f as is necessary for producing the desired maximum current.

In the examples illustrated in Figs. 2 and 3 the subsidiary generator d which supplies the controlling electromotive force and is driven by the motor we must be constructed in. such a way that it produces a comparatively high voltage for a small number of revolutions. And at full speed it must roduce a multiple of the said voltage, w ich value is so much the higher the more the re sistance of the rheostat r of the controlling generator a differs from that of the rheosta't s which is included in the exciting. c1 rcu1t and is connected to the controlling generator d. However such a voltage which is produced at full speed is objectionable by reason of the difficulty of insulation. Therefore the system is preferably so arranged that the field h of the controlling generator (1 is weakened at high speeds, and if desired completely thrown out of operation at the maximum speed. A system arranged according to this principle is-shown'in Fig. 4. The field winding h of the cont-rolling generator d connected with the motor m is not excited by a constant electromotive force, but its exciting voltage is decreased the more the speedof the motor m and of the controlling generator dis increased.

The reduction of the exciting voltage ot'v the controlling generator d can be effected in asimple way by supplying the electromotive force over a part of the resistance of the rheostat r the other part of which controls the exciting voltage for the field winding. f of the starting generator (1.

The subsidiary generator which has been used in the systems described in Figs. 2 to 4 for obtaining an exact harmony between the excitation of the-starting machine a and the speed of the driving motor m can be dispensed with by using the electromotive force of the driving motor m produced by the movement within the field as controlling electromotive force.- In systems heretofore designed this electromotive force could not be used, because the voltage at-the terminals does not merely depend on the number of revolutions, but is also a function of the v exciting cir'cuit,-tl1e resistance of the. armature of the motor w, and the resistances 'w and e0 Obviously betweenthe points 0 and ;0 there can be no difference in potential as long as the resistances are properly balanced and the armature of the motor is atrest, and it is immaterial what current passes through the armature of the motor. Whenthe motor rotates a voltmeter connected to these points shows a voltage which corresponds to the counter-electromotive force of the armature of the motor. To, the points 0, p

a resistance s is connected which is in s'eries with the field winding f.

Difi'erent from the VVheatstone bridge in which the points 0 and 79 have the same potential when the bridge is balanced the ratio of the resistances w? and 'w and the re- 'sistance 'w are, such, that between the points 0 and 79 there is such a'voltage, that the loss in voltage caused in the resistance sby the field current of the starting machine is ex actly balanced, as long as the speed of the motor m is exactly proportional to the field excitation of the starting dynamo a, so that there is no'balancing-current in the circuit connecting the points 0 and p to the exciting circuit 7. If however the speed of the motor, by, reason of its remanence or other conditions, should not-be exactly proportional to the loss'in Voltage caused in the resistance of the starting generator 11; a balancing current is set up which strengthens the field f if the speed of the motor is too small, and which weakens the same ifthe Y speed of the motor is too. high. {As ordi the speed of the motor needs control; l ng merely in the range 0t lower. speeds, .it is advisable under certain circumstancesto throw the resistances Q02 and w out of op cration in case of high speeds in order to avoid losses in energy. *It'is of course immaterial in which one of the two current v supplying conductors to the motor the resistance w or" the bridgeis included. If

necessary additional resistances may be in! cluded in the circuit.

Claims: 3

l.- The combination a' motor" and a generator connected in circuit "therewith, of

'a' field winding for I said generaton-and (means for compensatmg for the remanence of the generator.

2. The combinationwi th a motor and generator connected in circuit therewith, of

'. generator connected in circuit therewith, of" a field winding for said generator, and means controlled by the'speed of the motor for the remarience of the $5 for compensating a field winding for said generator, and automatically controlled means for-compensatingfor the remanence of the generator.

The combination with a motor-and a generator; 4

4. The combination with a motor and a I generator connected in circuit therewith, of

a field winding for said generator, and

means'fo-r insuring the control of the motor speed in accordance with the excitation of the generator field furnished by said'field winding.

5; The combination with a motor and a generator connected in circuit therewith, of

5 ai field winding for said generator, and

. igceegeee meansindependent of the main current for insuring the control of the motor speed in erator field.

6. The combination with a motor and a generator connected in circuit therewith, of a. field winding for said generator, means accordance with the excitation of the gen- .governing the generator field to vary the I the control of thermotor speed accordance with the gov'eming means 7. The combination with a motor and a speed of the motor, and means for insuring generator connected in circuit therewith, of

a field winding for said generator, and means for concurrently: impressing on said field winding an electromotive force adapted to set up an= exciting current said windtothe speed of said motor.

.8. The combination with a motor and a generator connectedin circuit therewith, of

ing, and an eiectromotive force proportional a compound field winding for said generator, and means for insuring, the control of the motor speed in accordance with th' main excitation of said winding. "'9; The combination with a motor and a a compound field winding for said generator,1-and' means for impressing'on themain field winding an elec'tromctive force adapted to fset'upan exciting current in said windgenerator connected. in circuit therewith, of

"ing, andan electromotive force proportional to the speed of said motor.

generator connected in circuit therewith, of a 'field winding, for said generator, "and 10. The combination with a motor and a loo means'fo'r compensatingfor the remanence field excitation; I

11. The combination with'a motor. and a generator connected in circuit therewith, of

' of the" generator at the lower limitsof a field winding for said generator, and means for insuring the control of'the vo1t-.

motor in accordance withth'e' excitation of said generator furnished biysaid field wind- I 12. The-combination with ,a motorand a generator connectedin circuit therewith, of

speed of the motor and connected withsaid field winding.

'ed toa source of current, and an auxiliary generator dnven in. accordance withjq'the age impressed'by said generator on said 14. The combination with a motor and a 1 a compoundfield windingfor said generator havingits main windingconnected to generator connected in circuit therewith, of

a source of current, andan auxiliary generator driven in'accordance with the s eedvof the motor and connected withthe mam field winding.

15.. The combination with a motor and a generator connected in circuit therewith of a fieldwinding for said generator, a di er-' I g generatorconnected inj'circuit therewith, of a a field winding for said generator, and

tial device connected in circuit with said winding, and separate sources of. current connected to said difierential device.

16.- The combination with a motor and a, generator connected in circuit therewithfi of I a field-winding for said generator, a di ential device.

' a field winding ential device connected in circuit with said winding, and a source at exciting current and a source ofigcurrentcontrolled b the speed of the motor connected 'to said-(E 17, The combinationiwi th -a motor and generator, connected in circuit therevt'ith, of

4 source of exciting current and a-source of controlling currentacting' difieren'tially on;

v difierentially on saidfield winding.

fier-' f I .In' testimony whereof I' have'jsigned my for said generator, and a I 18. The combination with a motor. and @125 generator connected-in circuit therewith, of a field winding for said generator, and a source of .excitin current and a source of current controll'e by the motor speed acting ,19. The combination with a motor and a means forjcompensating for boththe positive andfnegative'remanance of the gener- 35 ator.

' v20'. The" combination with a motor and a generator connected in circuit therewith, of

a field winding for. said generator, and means for compensating for the remanence 40 of the generator at various loads and speeds.

name to this specification in the presence of v two subscribing witnesses. s f f LCHRISTIAN KRAMER. 

